Packet Energy Transfer In-Line Communications

ABSTRACT

Data is communicated between a digital power transmitter and one or more digital power receivers over a transmission line comprising positive and negative conductors. If the transmitter is sending data to the receiver, a first transmitter electrical switch is selectively operated to increase electrical charge in the transmission-line capacitance. If the receiver is sending data to the transmitter, a first receiver electrical switch is selectively operated to increase electrical charge in the transmission-line capacitance.

RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.61/931,678, filed 26 Jan. 2014, the entire content of which isincorporated herein by reference.

BACKGROUND

Digital electric power can be characterized as any power format whereelectrical power is distributed in discrete, controllable units ofenergy. Packet Energy Transfer (PET) is a new type digital electricpower protocol that has been disclosed in U.S. Pat. No. 8,781,637 (Eaves2012).

The primary discerning factor in a digital power transmission systemcompared to traditional, analog power systems is that the electricalenergy is separated into discrete units, and individual units of energycan be associated with analog and/or digital information that can beused for the purposes of optimizing safety, efficiency, resiliency,control or routing.

As described by Eaves 2012, a source controller and a load controllerare connected by power transmission lines. The source controller ofEaves 2012 periodically isolates (disconnects) the power transmissionlines from the power source and analyzes, at a minimum, the voltagecharacteristics present at the source controller terminals directlybefore and after the lines are isolated. The time period when the powerlines are isolated was referred to by Eaves 2012 as the “sample period”and the time period when the source is connected is referred to as the“transfer period”. The rate of rise and decay of the voltage on thelines before, during and after the sample period reveal if a faultcondition is present on the power transmission lines. Measurable faultsinclude, but are not limited to, short circuit, high line resistance orthe presence of an individual who has improperly come in contact withthe lines. Eaves 2012 also describes digital information that may besent between the source and load controllers over the power transmissionlines to further enhance safety or provide general characteristics ofthe energy transfer, such as total energy, or the voltage at the loadcontroller terminals. Since the energy in a PET system is transferred asdiscrete quantities, or quanta, it can be referred to as “digitalpower”.

Eaves 2012 disclosed the method of modulating and demodulating acommunication carrier signal on the same power lines that carry theelectrical power. The technique is well known to those skilled in theindustry and often referred to as “power line communications”, “powerline carrier communications” or “carrier current communications”. Themethod disclosed by Eaves 2012 did not identify if the communicationwould occur during the time when the source and load devices aretransferring power (transfer period) or if it would occur during thetime when the source is isolated from the transmission lines (sampleperiod).

The present invention discloses a method and apparatus for communicationonly during the sample period of the digital power waveform. During thesample period, the line is isolated, and there is no interference in thecommunications stream due to the normal transfer of power from thesource to load devices. This provides the opportunity forcost-effective, robust, relatively high rate communications thatminimize hardware and software requirements.

Although the present specification is focused on the application of theinvention to a digital power transmission system, the disclosed methodcan be implemented for communication between generic devices withoutrequiring the transfer of power.

SUMMARY

Methods for communicating data between a digital power transmitter andone or more digital power receivers are described herein, where variousembodiments of the methods and apparatus for performing the method mayinclude some or all of the elements, features and steps described below.

In a method for communicating data between a digital power transmitterand one or more digital power receivers over a transmission linecomprising positive and negative conductors, wherein the transmissionline has electrical properties that include at least a finiteline-to-line capacitance and at least a finite line-to-line resistance,the method includes: (a) if the transmitter is sending data to thereceiver, selectively operating a first transmitter electrical switch toincrease electrical charge in the transmission-line capacitance byconnecting the transmission line to a transmitter voltage source througha finite resistance or by operating a second transmitter electricalswitch to decrease electrical charge by connecting the positive andnegative conductors to each other through a finite resistance such thatthe rate of change in transmission-line voltage alternates between afirst voltage slope value and a second voltage slope value, wherein thechange in voltage slope is detected and decoded by the receiver toreproduce the data being sent by the transmitter; and (b) if thereceiver is sending data to the transmitter, selectively operating afirst receiver electrical switch to increase electrical charge in thetransmission-line capacitance by connecting the transmission lines to areceiver voltage source through a finite resistance or by operating asecond receiver electrical switch to decrease electrical charge byconnecting the positive and negative conductors to each other through afinite resistance such that the rate of change in transmission-linevoltage alternates between a first voltage slope value and a secondvoltage slope value, wherein the change in voltage slope is detected anddecoded by the transmitter to reproduce the data being sent by thetransmitter.

The transmitter voltage source can be connected to the transmission linethrough a series resistance small enough to cause a rapid increase intransmission-line voltage. The detection of the rapid increase by thetransmitter or receiver can be used as a timing reference point forsetting the relative times to sample and determine the voltage slopevalues that signify logic states.

During the time when the receiver is communicating to the transmitter,the transmitter can act to connect the transmission line to thetransmitter voltage source through a first resistor value; and the loadside can simultaneously connect the transmission-line conductors to eachother through a second resistor value, thus forming a voltage dividerthat creates a third voltage slope value that is detected by thetransmitter. Using the analogy of a stop watch, the rapid voltagetransition point is where the stopwatch is reset to zero and is used toset the schedule for when activities occur. The activities are“relative” to the reset time on the watch.

The transmitter already knows when the transition happens since it wasthe one that initiated it, but the receiver must sense the sharp voltagetransition on the transmission line to synchronize with the transmitter.

If the transmitter is sending data to the receiver, only one of the twotransmitter electrical switches may be implemented such that the rate ofchange in transmission-line voltage alternates between a first voltageslope value when the one transmitter electrical switch is closed and asecond voltage slope value when the one transmitter electrical switch isopen, wherein the change in voltage slope can be detected and decoded bythe receiver to reproduce the data being sent by the transmitter.

If the receiver is sending data to the transmitter, only one of the tworeceiver electrical switches may be implemented such that the rate ofchange in transmission-line voltage alternates between a first voltageslope value when the one receiver electrical switch is closed and asecond voltage slope value when the one receiver electrical switch isopen, wherein the change in voltage slope can be detected and decoded bythe transmitter to reproduce the data being sent by the receiver.

The transmitter or receiver can execute an encoding algorithm for apredetermined number of original data bits to be transmitted, whereinthe input to the encoding algorithm is the predetermined number oforiginal bits and the output of the algorithm is a larger number ofoptimized bits that are chosen to maintain the transmission-line voltagebetween predetermined upper and lower voltage boundaries, and whereinthe optimized bits can then be decoded at the receiver back to thepredetermined number of original bits.

The transmitter or receiver can execute an algorithm to calculate thecapacitance of the transmission line based on a measurement of the rateof decay of transmission-line voltage and a predetermined value ofline-to-line resistance.

The calculated capacitance value of the transmission line and thepredetermined line-to-line resistance can be used as inputs to analgorithm to predict the time when the transmission-line voltage willdecay to an optimal value for supporting the transmission of data.

The transmitter maintains predetermined acceptable values fortransmission-line voltage. Voltages outside of the acceptable valuesindicate a fault condition, and the transmitter can execute an algorithmto adjust the acceptable values based on the characteristics of the datatransmitted from the transmitter to the receiver or from the receiver tothe transmitter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of a representative digital power system.

FIG. 2 is a voltage plot showing the difference between normal operationand a fault.

FIG. 3 is an illustration of a digital power system when switch S2 isclosed.

FIG. 4 is an illustration of a digital power system when switches S2 andS4 are closed.

FIG. 5 is a voltage plot showing an embedded byte of data on thetransmission lines to be read by the receiver.

In the accompanying drawings, like reference characters refer to thesame or similar parts throughout the different views; and apostrophesare used to differentiate multiple instances of the same or similaritems sharing the same reference numeral. The drawings are notnecessarily to scale; instead, emphasis is placed upon illustratingparticular principles in the exemplifications discussed below.

DETAILED DESCRIPTION

The foregoing and other features and advantages of various aspects ofthe invention(s) will be apparent from the following, more-particulardescription of various concepts and specific embodiments within thebroader bounds of the invention(s). Various aspects of the subjectmatter introduced above and discussed in greater detail below may beimplemented in any of numerous ways, as the subject matter is notlimited to any particular manner of implementation. Examples of specificimplementations and applications are provided primarily for illustrativepurposes.

Unless otherwise herein defined, used or characterized, terms that areused herein (including technical and scientific terms) are to beinterpreted as having a meaning that is consistent with their acceptedmeaning in the context of the relevant art and are not to be interpretedin an idealized or overly formal sense unless expressly so definedherein. Percentages or concentrations expressed herein can representeither by weight or by volume. Processes, procedures and phenomenadescribed below can occur at ambient pressure (e.g., about 50-120kPa—for example, about 90-110 kPa) and temperature (e.g., −20 to 50°C.—for example, about 10-35° C.) unless otherwise specified.

Although the terms, first, second, third, etc., may be used herein todescribe various elements, these elements are not to be limited by theseterms. These terms are simply used to distinguish one element fromanother. Thus, a first element, discussed below, could be termed asecond element without departing from the teachings of the exemplaryembodiments.

Spatially relative terms, such as “above,” “below,” “left,” “right,” “infront,” “behind,” and the like, may be used herein for ease ofdescription to describe the relationship of one element to anotherelement, as illustrated in the figures. It will be understood that thespatially relative terms, as well as the illustrated configurations, areintended to encompass different orientations of the apparatus in use oroperation in addition to the orientations described herein and depictedin the figures. For example, if the apparatus in the figures is turnedover, elements described as “below” or “beneath” other elements orfeatures would then be oriented “above” the other elements or features.Thus, the exemplary term, “above,” may encompass both an orientation ofabove and below. The apparatus may be otherwise oriented (e.g., rotated90 degrees or at other orientations) and the spatially relativedescriptors used herein interpreted accordingly.

Further still, in this disclosure, when an element is referred to asbeing “on,” “connected to,” “coupled to,” “in contact with,” etc.,another element, it may be directly on, connected to, coupled to, or incontact with the other element or intervening elements may be presentunless otherwise specified.

The terminology used herein is for the purpose of describing particularembodiments and is not intended to be limiting of exemplary embodiments.As used herein, singular forms, such as “a” and “an,” are intended toinclude the plural forms as well, unless the context indicatesotherwise. Additionally, the terms, “includes,” “including,” “comprises”and “comprising,” specify the presence of the stated elements or stepsbut do not preclude the presence or addition of one or more otherelements or steps.

Additionally, the various components identified herein can be providedin an assembled and finished form; or some or all of the components canbe packaged together and marketed as a kit with instructions (e.g., inwritten, video or audio form) for assembly and/or modification by acustomer to produce a finished product.

A representative digital power system, as originally described in Eaves2012, is shown in FIG. 1. The system comprises a source 1 and at leastone load 2. The PET protocol is initiated by operating switch means 3 toperiodically disconnect the source 1 from the power transmission lines.When the switch is in an open (non-conducting) state, the lines are alsoisolated from any stored energy that may reside at the load 2 byisolation diode (D_(L)) 4.

Eaves 2012 offered several versions of alternative switches that couldreplace diode (D_(L)) 4 but all versions would have similar resultsrelated to the present invention. Capacitor (C₃) 5 is representative ofan energy storage element on the load side of the circuit.

The transmission lines have inherent line-to-line resistance (R₄) 6 andcapacitance (C₁) 7. The PET system architecture, as described by Eaves2012, adds additional line-to-line resistance (R₃) 8 and capacitance(C₂) 9. At the instant switch (S1) 3 is opened, capacitor (C₁) 7 andcapacitor (C₂) 9 have stored charge that decays at a rate that isinversely proportional to the parallel resistance comprising (R₄) 6 and(R₃) 8. Capacitor (C₃) 5 does not discharge through resistor (R₃) 8 andresistor (R₄) 6 due to the reverse blocking action of diode (D_(L)) 4.The amount of charge contained in capacitor (C₁) 7 and capacitor (C₂) 9is proportional to the voltage across them and can be measured at points16 and 17 by a source controller 18 or load controller 19.

As described in Eaves 2012, a change in the rate of decay of the energystored in capacitor (C₁) 7 and capacitor (C₂) 9 can indicate that thereis a cross-line fault on the transmission lines. The difference betweennormal operation and a fault, as presented by Eaves 2012, is illustratedin FIG. 2.

Referring again to FIG. 1, the combination of switch (S1) 3, sourcecontroller 18, resistor (R₁) 10, switch (S3) 13, and resistor (R₃) 8 canbe referred to as a transmitter 20. The combination of switch (S4) 15,resistor (R₅) 14, load controller 19, diode (D_(L)) 4, capacitor (C₂) 9,and capacitor (C₃) 5 can be referred to as a receiver 21.

Referring again to FIG. 1, a method is disclosed that exploits thesampling period described in Eaves 2012 as a time to embed communicationdata on the same transmission lines that are used for power transfer.This is accomplished by modulating the stored charge that is present oncapacitor (C₁) 7 and on capacitor (C₂) 9 during the sampling period.

A simple method is disclosed for modulating the stored charge through apull-up or pull-down resistor circuit that can add or subtractincrements of charge to the transmission line capacitance at high speed.An example of a pull-up circuit is represented by resistor (R₁) 10 andswitch (S2) 11 of FIG. 1. Pull-down circuits are represented by resistor(R₂) 12 and switch (S3) 13 on the transmitter side and resistor (R₅) 14and switch (S4) 15 on the receiver side.

Uni-directional communications is defined as communication only from thetransmitter 20 to the receiver 21 or from the receiver to thetransmitter. This would require only a single pull-up or pull-downcircuit. For uni-directional communication from the transmitter 20 tothe receiver 21, the pull-up circuit formed by resistor (R₁) 10 andswitch (S2) 11 allows the transmitter 20 to embed data on thetransmission lines that could then be read by the receiver 21 at loadvoltage sensing point 17. Alternatively, the pull-down circuit formed byresistor (R₂) 12 and switch (S3) 13 also allows the transmitter 20 toembed data on the transmission lines that can then be read by thereceiver 21.

For uni-directional communication from the receiver 21 to thetransmitter 20, the pull-down circuit formed by resistor (R₅) 14 andswitch (S4) 15 can be employed to allow the transmitter 20 to detect thedata at voltage sensing point 16. The receiver 21 can also use a pull-upcircuit rather than a pull-down circuit; but, for simplicity, thisoption is not shown in the figure.

Since the primary limitation on data transfer rate is the transmissionline capacitance the optimal configuration for the fastest datatransmission would be to include pull-up and pull-down circuits in boththe transmitter 20 and receiver 21 circuitry, but this is adetermination to be made on several factors that would include systemcost, volume and reliability.

Transmitter Sending a Byte of Data to a Receiver

The activation of a pull-up or pull-down circuit has the effect ofchanging the slope of the normal decay rate of the transmission linecapacitance. In a particular embodiment, referring to FIG. 1 the pull-upcircuit in transmitter 20 comprises resistor (R₁) 10 and switch (S1) 11can be used to embed a byte of data 30 of FIG. 5 on the transmissionlines to be read by receiver 21. In FIG. 5, the leading “0” bit 32 isgenerated by not activating the source side pull-up circuit, resultingin the voltage decay slope continuing unmodified. The zero bit is usedto sample the existing slope of decay in the transmission line voltage.Slope calculation can be performed in hardware using differentiatorcircuits, or it may be performed in software by taking storing a minimumof two consecutive voltage sample and calculating the relative slopebetween them.

In the next bit period, the pull-up circuit is not activated to generatea logic “0” then a “1” is generated by activating the pull-up circuit.The process of selectively activating or not activating the pull-upcircuit continues until the entire byte is transferred by the sourceside to the load side.

Receiver Circuit Receiving a Byte of Data from the Transmitter

In a particular embodiment, the transmitter 20 receives a byte of datafrom the receiver 21 by activating its pull-up circuit resistor (R₁) 10and switch (S2) 11 of FIG. 1, while the receiver 21 simultaneouslyactivates its pull-down circuit comprising resistor (R₅) 14 and switch(S4) 15 to generate a logic “0”. To generate a logic “1”, thetransmitter 20 activates its pull-up circuit, while the receiver 21simultaneously does not activate its pull-down circuit.

To determine when to activate the circuits, the data frame issynchronized with the rising edge that occurs at the end of the lastsample period 31 of FIG. 5. The source controller 18 of FIG. 1 isinherently aware of the synchronization point since it is the deviceactivating the disconnect switch, but the load controller 19 needs adefinitive method to synchronize its data transmission and reception.Rising edge 31 of FIG. 5 is sharp and distinctive because thetransmitter 20 of FIG. 1 is at that time directly connecting the sourcepotential to the transmission line with the lowest possible resistancein between in order to maximize efficiency. In a particular embodiment,the load controller 19 through software or hardware detects the largepositive change in voltage and steep slope, indicating the end of thesample period and beginning of the next frame of data transmission. Theload and source controllers 19 and 18 wait a predetermined time afterthe synchronization point to embed the first bit of data. Alternatively,a change in voltage at the beginning of the sample period 33 of FIG. 5can be used as a synchronization point. The voltage slope at point 33 isless distinctive than point 31 but has the advantage of being closer intime to the point where the data will be embedded and thus may be moresuitable for processors with less accurate timing capability.

Selecting the Start Time for Data Transmission

Referring to FIG. 5, it should be noted that there is a strategy toselecting the portion of the sample period where the data stream will beembedded on the transmission lines. If the transmission-line voltageduring the sample period, as seen on the source side circuitry, is toohigh or too low, then the slope change caused by activating the pull-upor pull-down circuits on the source side or load side will be smallerand less detectable by the corresponding voltage sensing circuitry inthe transmitter 20 or receiver 21.

Referring to FIGS. 3 and 4, there is an optimal voltage range to performthe data transmission that is determined by the steady state DC voltagelevels that occur when switch (S2) 11 is closed and switch (S4) 15 isopen, as in FIG. 3, and when switch (S2) is closed and switch (S4) isalso closed, as in FIG. 4. These two states represent all of thepreviously described conditions where the transmitter 20 is transmittinga logic “1” or “0” to the receiver 21 and where the receiver 21 istransmitting a “1” or “0” to the transmitter 20 circuitry.

Again referring to FIG. 3, the upper side of the voltage range isdefined approximately as:

V _(o) ≈V _(s) ·R ₃/(R ₁ +R ₃),

and the lower side of the range is defined in FIG. 4 approximately as:

V _(o) ≈V _(s) ·R ₅/(R ₁ +R ₅).

Since the variables in the equations are known in advance by the sourcecontroller 18, the transmitter 20 can execute an algorithm in its sourcecontroller 18 to select the beginning time for the start of its datatransmission based on the expected decay rate in the transmission linevoltage. The decay rate is chiefly governed by the line-to-lineresistance and line-to-line capacitance. The line-to-line resistance isknown in advance as part of the system design and the line-to-linecapacitance can be measured by the source controller 20 or loadcontroller 21 by measuring the rate of decay of the transmission linevoltage and applying mathematics well known to those skilled in the artfor the decay rate of a resistive-capacitive circuit.

8b/9b Encoding of Data Transmission

In telecommunications data transmission, a technique well known to theindustry is 8b/9b encoding. 8b/9b encoding is method that maps 8-bitsymbols to 9-bit symbols to achieve DC-balance in the physicaltransmission medium. This means that the difference between the numberof logic “1s” and “0s” in the data transmission is kept to a minimum.Because communication protocols, such as Ethernet, use isolationtransformers, an imbalance in the number of positive and negative logicstates can result in an undesirable DC magnetic flux in the transformercore and reduced performance. There are variations of 8b/9b, such as8b/10b, that result in closer balance of logic states, albeit at theexpense of more bits needed for each symbol.

Methods described herein draw on the concept of 8b/9b encoding for thepurpose of optimizing the placement of the data stream within the upperand lower voltage boundaries set by the pull-up/pull-down circuitrydescribed above. More specifically the method employs 8b/9b encoding tocreate a symbol table that accounts for the known electrical variablesin the digital power transmission system to keep the transmission-linevoltage during data transmission centered within the upper and lowervoltage boundaries. Since the transmission lines are already biased todecay rather than rise during the sample period, the symbol table is setto provide an upward bias in compensation.

Other Embodiments

In existing implementations of packet energy transfer, there arepredetermined fault trip-point values for the amount of decay in thetransmission line voltage during the sample period. For bettersensitivity of line faults where in-line data transmission is beingperformed, a particular embodiment can include adjusting the faulttrip-points based on the amount of change caused in thetransmission-line voltage due to the transmission of data. For example,if the line voltage is normally allowed to drop to 300 Vdc before beingconsidered a fault condition, the trip-point can be raised to 310 Vdc toaccount for a data transmission instance that biased the decay voltageupwards during the sample period.

In another particular embodiment, a single digital power transmitter 20can communicate with multiple receivers, where each receiver would beprogrammed with an address code. The data transmission protocol includesthe address of the receiver when sending a command if the commandinvolved a particular instruction for that receiver.

In describing embodiments of the invention, specific terminology is usedfor the sake of clarity. For the purpose of description, specific termsare intended to at least include technical and functional equivalentsthat operate in a similar manner to accomplish a similar result.Additionally, in some instances where a particular embodiment of theinvention includes a plurality of system elements or method steps, thoseelements or steps may be replaced with a single element or step;likewise, a single element or step may be replaced with a plurality ofelements or steps that serve the same purpose. Further, where parametersfor various properties or other values are specified herein forembodiments of the invention, those parameters or values can be adjustedup or down by 1/100^(th), 1/50^(th), 1/20^(th), 1/10^(th), ⅕^(th),⅓^(rd), ½, ⅔^(rd), ¾^(th), ⅘^(th), 9/10^(th), 19/20^(th), 49/50^(th),99/100^(th), etc. (or up by a factor of 1, 2, 3, 4, 5, 6, 8, 10, 20, 50,100, etc.), or by rounded-off approximations thereof, unless otherwisespecified. Moreover, while this invention has been shown and describedwith references to particular embodiments thereof, those skilled in theart will understand that various substitutions and alterations in formand details may be made therein without departing from the scope of theinvention. Further still, other aspects, functions and advantages arealso within the scope of the invention; and all embodiments of theinvention need not necessarily achieve all of the advantages or possessall of the characteristics described above. Additionally, steps,elements and features discussed herein in connection with one embodimentcan likewise be used in conjunction with other embodiments. The contentsof references, including reference texts, journal articles, patents,patent applications, etc., cited throughout the text are herebyincorporated by reference in their entirety; and appropriate components,steps, and characterizations from these references may or may not beincluded in embodiments of this invention. Still further, the componentsand steps identified in the Background section are integral to thisdisclosure and can be used in conjunction with or substituted forcomponents and steps described elsewhere in the disclosure within thescope of the invention. In method claims, where stages are recited in aparticular order—with or without sequenced prefacing characters addedfor ease of reference—the stages are not to be interpreted as beingtemporally limited to the order in which they are recited unlessotherwise specified or implied by the terms and phrasing.

What is claimed is:
 1. A method for communicating data between a digitalpower transmitter and one or more digital power receivers over atransmission line comprising positive and negative conductors, whereinthe transmission line has electrical properties that include at least afinite line-to-line capacitance and at least a finite line-to-lineresistance, the method comprising: a) if the transmitter is sending datato the receiver, selectively operating a first transmitter electricalswitch to increase electrical charge in the transmission-linecapacitance by connecting the transmission-line to a transmitter voltagesource through a finite resistance or by operating a second transmitterelectrical switch to decrease electrical charge by connecting thepositive and negative conductors to each other through a finiteresistance such that the rate of change in transmission-line voltagealternates between a first voltage slope value and a second voltageslope value, wherein the change in voltage slope is detected and decodedby the receiver to reproduce the data being sent by the transmitter; andb) if the receiver is sending data to the transmitter, selectivelyoperating a first receiver electrical switch to increase electricalcharge in the transmission-line capacitance by connecting thetransmission lines to a receiver voltage source through a finiteresistance or by operating a second receiver electrical switch todecrease electrical charge by connecting the positive and negativeconductors to each other through a finite resistance such that the rateof change in transmission-line voltage alternates between a firstvoltage slope value and a second voltage slope value, wherein the changein voltage slope is detected and decoded by the transmitter to reproducethe data being sent by the receiver.
 2. The method of claim 1, whereinthe transmitter voltage source is connected to the transmission linethrough a series resistance small enough to cause a rapid increase intransmission-line voltage, the method further comprising using thedetection of the rapid increase by the transmitter or receiver as atiming reference point for setting relative times to sample anddetermine the voltage slope values that signify logic states.
 3. Themethod of claim 1, wherein, during the time when the receiver iscommunicating to the transmitter, the transmitter acts to connect thetransmission line to the transmitter voltage source through a firstresistor value; and the load side simultaneously connects thetransmission-line conductors to each other through a second resistorvalue, thus forming a voltage divider that creates a third voltage slopevalue that is detected by the transmitter.
 4. The method of claim 1,wherein, if the transmitter is sending data to the receiver, only one ofthe two transmitter electrical switches is implemented such that therate of change in transmission-line voltage alternates between a firstvoltage slope value when the one transmitter electrical switch is closedand a second voltage slope value when the one transmitter electricalswitch is open, wherein the change in voltage slope is detected anddecoded by the receiver to reproduce the data being sent by thetransmitter.
 5. The method of claim 1, wherein, if the receiver issending data to the transmitter, only one of the two receiver electricalswitches is implemented such that the rate of change intransmission-line voltage alternates between a first voltage slope valuewhen the one receiver electrical switch is closed and a second voltageslope value when the one receiver electrical switch is open, wherein thechange in voltage slope is detected and decoded by the transmitter toreproduce the data being sent by the receiver.
 6. The method of claim 1,wherein the transmitter or receiver executes an encoding algorithm for apredetermined number of original data bits to be transmitted, whereinthe input to the encoding algorithm is the predetermined number oforiginal bits and the output of the algorithm is a larger number ofoptimized bits that are chosen to maintain the transmission-line voltagebetween predetermined upper and lower voltage boundaries, and whereinthe optimized bits are then decoded at the receiver back to thepredetermined number of original bits.
 7. The method of claim 1, whereinthe transmitter or receiver executes an algorithm to calculate thecapacitance of the transmission line based on a measurement of the rateof decay of transmission-line voltage and a predetermined value ofline-to-line resistance.
 8. The method of claim 7, wherein thecalculated capacitance value of the transmission line and thepredetermined line-to-line resistance is used as inputs to an algorithmto predict the time when the transmission-line voltage will decay to anoptimal value for supporting the transmission of data.
 9. The method ofclaim 1, wherein the transmitter maintains predetermined acceptablevalues for transmission-line voltage, and wherein voltages outside ofthe acceptable values indicate a fault condition, and wherein thetransmitter executes an algorithm to adjust the acceptable values basedon the characteristics of the data transmitted from the transmitter tothe receiver or from the receiver to the transmitter.
 10. A method forcommunicating data between a digital power transmitter and one or moredigital power receivers over a transmission line comprising positive andnegative conductors, wherein the transmission line has electricalproperties that include at least a finite line-to-line capacitance andat least a finite line-to-line resistance, the method comprising: a) ifthe transmitter is sending data to the receiver, selectively addingelectrical charge to the transmission line capacitance by connecting thetransmission line to a transmitter power source or subtracting electriccharge from the transmission line capacitance by connecting the positiveand negative conductors to a transmitter power sink, such that the rateof change in transmission line voltage alternates between a firstvoltage slope value and a second voltage slope value, wherein the changein voltage slope is detected and decoded by the receiver to reproducethe data being sent by the transmitter; and b) if the receiver issending data to the transmitter, selectively adding electric charge tothe transmission-line capacitance by connecting the transmission linesto a receiver power source or by selectively subtracting electric chargefrom the transmission line capacitance by connecting the conductors to areceiver power sink, such that the rate of change in transmission-linevoltage alternates between a first voltage slope value and a secondvoltage slope value, wherein the change in voltage slope is detected anddecoded by the transmitter to reproduce the data being sent by thereceiver.
 11. The method of claim 10, wherein the transmitter powersource is connected to the transmission line through a series resistancesmall enough to cause a rapid increase in transmission-line voltage, themethod further comprising using the detection of the rapid increase bythe transmitter or receiver as a timing reference point for settingrelative times to sample and determine the voltage slope values thatsignify logic states.
 12. The method of claim 10, wherein, during thetime when the receiver is communicating to the transmitter, thetransmitter acts to connect the transmission line to the transmittervoltage source through a first resistor value; and the load sidesimultaneously connects the transmission-line conductors to each otherthrough a second resistor value, thus forming a voltage divider thatcreates a third voltage slope value that is detected by the transmitter.13. The method of claim 10, wherein, if the transmitter is sending datato the receiver, only one method of either adding or subtracting chargeis implemented such that the rate of change in transmission-line voltagealternates between a first voltage slope value when the one method ofadding or subtracting charge is implemented and a second voltage slopewhere charge is not being added or subtracted, wherein the change involtage slope is detected and decoded by the receiver to reproduce thedata being sent by the transmitter.
 14. The method of claim 10, wherein,if the receiver is sending data to the transmitter, only one method ofeither adding or subtracting charge is implemented such that the rate ofchange in transmission-line voltage alternates between a first voltageslope value when the one method of adding or subtracting charge isimplemented and a second voltage slope where charge is not being addedor subtracted, wherein the change in voltage slope is detected anddecoded by the transmitter to reproduce the data being sent by thereceiver.
 15. The method of claim 10, wherein the transmitter orreceiver executes an encoding algorithm for a predetermined number oforiginal data bits to be transmitted, wherein the input to the encodingalgorithm is the predetermined number of original bits and the output ofthe algorithm is a larger number of optimized bits that are chosen tomaintain the transmission-line voltage between predetermined upper andlower voltage boundaries, and wherein the optimized bits are thendecoded at the receiver back to the predetermined number of originalbits.
 16. The method of claim 10, wherein the transmitter or receiverexecutes an algorithm to calculate the capacitance of the transmissionline based on a measurement of the rate of decay of transmission-linevoltage and a predetermined value of line-to-line resistance.
 17. Themethod of claim 16, wherein the calculated capacitance value of thetransmission line and the predetermined line-to-line resistance is usedas inputs to an algorithm to predict the time when the transmission-linevoltage will decay to an optimal value for supporting the transmissionof data.
 18. The method of claim 10, wherein the transmitter maintainspredetermined acceptable values for transmission-line voltage, andwherein voltages outside of the acceptable values indicate a faultcondition, and wherein the transmitter executes an algorithm to adjustthe acceptable values based on the characteristics of the datatransmitted from the transmitter to the receiver or from the receiver tothe transmitter.